August 23, 2016

Prehistoric Marsupial Lion Was The Size Of A Squirrel

Vinegar is
a handy liquid to have around. You can use it to clean your computer mouse,
wipe down your blinds, and remove carpet stains. Or, even better, you can use
it to discover some seriously cool extinct animals.

Acetic
acid—one of vinegar’s main constituents—is commonly used as a chemical
treatment to unlock delicate fossils from their rocky shackles. Recently,
paleontologists in a remote corner of Australia used the procedure to extract
the teeth of two long-dead mammal species from blocks of limestone.

Though the
teeth are the only remains of the newly discovered species, we can glean plenty
of details from a set of chompers. As paleontologist Steve Wroe says, “you can
get a hell of a lot of information from a single tooth!”

For
starters, one fossil jaw turned out to be a new addition to a bizarre family of
meat-eating mammals called the marsupial lions. But unlike its previously
discovered cousins, the new pouched creature was exceptionally tiny, coming in
at about the size of a grey squirrel.

“This
animal was just so small—it’s quite extraordinary,” says Anna Gillespie, the
University of New South Wales paleontologist who found and identified the new
species. “To me, it’s quite stunning.

Marsupial lions belong to an extinct
prehistoric family that is most closely related to modern koalas and wombats.
The family currently includes nine species, and its most famous member is Thylacoleo
carnifex.(Tasmanian Tiger).

Thylacoleo, which roamed what
is now Australia as recently as 46,000 years ago, is known for its extremely
powerful bite: Pound for pound, its jaws packed more force than a modern lion
or hyena bite.

The new
addition to the family, Microleo attenboroughi, was named in honor of
the renowned naturalist David Attenborough. It is a diminutive version of T.
carnifex that lived around 18 million years ago, according to the study
published in the July edition of Palaeontologia Electronica. Weighing in
at approximately 1.3 pounds (600 grams), Microleo was considerably
smaller than its 220-pound (100-kilogram) relative.

Gillespie and her team identified the species
using parts of its jaw recovered from limestone deposits at the Riversleigh
World Heritage Area, a famous fossil site in Australia.

The
fossilized teeth became exposed through the millennia as water slowly dissolved
the limestone surrounding them. A volunteer found a portion of the tooth
protruding from a rock block, and it was fully freed when Gillespie used the
acetic acid to eat away the remaining limestone.

Teeth are
commonly used to identify species, especially mammals, says Wroe, a paleontologist
at the University of New England in Australia who was not involved in the
study. The shapes of the teeth, in particular, can reveal what the animal most
likely ate and other clues to how it fit into its ancient ecosystem.

“The molar teeth are typically more informative
than other teeth because they are more complex,” he says. Based on its
teeth—premolars and molars from both the left and right jaw—Microleo was
probably an arboreal predator that dined on a variety of other small creatures.

“It was
likely living up in the trees having a good time and eating all the small
animals,” Gillespie says.

For now,
though, the team still has plenty of unanswered questions, because the teeth
that Gillespie found are the only evidence that this Lilliputian carnivore ever
existed. This could indicate the species was rare when it lived, or it could
just mean Gillespie and her team need to keep looking for additional fossils,
which is no problem for the self-described discovery junkie.

“I just
find it really intriguing that this is the only specimen we have,” she says.
“You just want to go out and find more, and keep looking and looking. To get a
skull would be fabulous.”

The other pearly white pulled from Australian
limestone belonged to another new marsupial species: Whollydooleya
tomnpatrichorum. The genus name references the site of the find—Wholly
Dooley Hill—and the species name is a shout-out to longtime Riversleigh
researchers Tom and Pat Rich.

Michael
Archer, a National Geographic grant recipient, worked with Gillespie, her Microleo
co-author Suzanne Hand, and others to describe the new marsupial in the Memoirs
of Museum Victoria.

While Microleo was unique for being
petite, Whollydooleya stands out for its extreme dentition,
specifically, its blade-like teeth.

While the
team found only one tooth, its shape indicates the animal was a
hypercarnivore—a flesh-eating creature whose diet consisted of at least 75
percent meat. The raised points on the crown, known as primary cusps, are
interspersed with shearing enamel blades, a feature that, according to Wroe, is
only useful for cutting meat.

To Archer,
the tooth’s form also suggests that the creature would have been safe from bad
breath: Their distinct shape would have effectively cleared out rotting food
particles that can cause halitosis.

Whoolydooleya, which lived about 12 million to five
million years ago, was placed in the Dasyuridae family, which includes over 60
species of mostly small and mouse-like marsupials, including the Tasmanian
devil.

However,
Archer says that the new species represents a group of carnivorous marsupials
that were not previously known. The researchers estimate that Whoolydooleya
was about 50 pounds (23 kilograms), or two to three times the size of the
modern Tasmanian devil. With its nasty teeth and large frame, Archer believes
it would have been a formidable opponent.

“It
probably would have been the ‘king of beasts’ within its home range,” he
writes, “able to catch and gobble pretty much any other animal that took its
fancy.”

However, Whoolydooleya
would not have been dining on Microleo, as the two species are separated
by millions of years. Still, looking at both fossil animals together can tell
the researchers a lot about changes in Australia’s ancient climate.

Neville’s
Garden, the site of the Microleo find, contains stalagmites preserved in
fossil material and is believed to have been a cave pool in a rich, diverse
rain forest environment.But the
younger sediments at Wholly Dolly Hill suggest that the hypercarnivore was
buried during a drier time. Combined, the fossils corroborate the theory that
Australia transitioned from a wet, humid climate to its arid state during the
Miocene.

As
scientists find more fossils around Riversleigh—particularly other small to
medium-size animals—they will be able to further piece together what was
happening as Australia dried out. Figuring out how life responded to a changing
ancient climate is essential to helping us understand modern extinctions,
especially in the face of accelerated climate change.

As Archer
notes, we don’t know what caused Microleo and Whollydooleya to go
extinct, but “climate change … has always been the primary reason for
extinctions.”